Organic light-emitting diode (OLED) devices, also referred to as organic electro-luminescent (EL) devices, have numerous well-known advantages over other flat-panel display devices currently in the market place. Among these advantages are brightness of light emission, relatively wide viewing angle, and reduced electrical power consumption compared to, for example, liquid crystal displays (LCDs) using back-lighting.
Applications of OLED devices include active-matrix image displays, passive-matrix image displays, and area lighting devices such as, for example, selective desktop lighting. Irrespective of the particular OLED device configuration tailored to these broad fields of applications, all OLEDs function on the same general principles. An organic electro-luminescent (EL) medium structure is sandwiched between two electrodes. At least one of the electrodes is light transmissive. These electrodes are commonly referred to as an anode and a cathode in analogy to the terminals of a conventional diode. When an electrical potential is applied between the electrodes so that the anode is connected to the positive terminal of a voltage source and the cathode is connected to the negative terminal, the OLED is said to be forward-biased. Positive charge carriers (holes) are injected from the anode into the EL medium structure, and negative charge carriers (electrons) are injected from the cathode. Such charge carrier injection causes current flow from the electrodes through the EL medium structure. Recombination of holes and electrons within a zone of the EL medium structure results in emission of light from this zone that is, appropriately, called the light-emitting zone or interface. The emitted light is directed towards an observer, or towards an object to be illuminated, through the light-transmissive electrode. If the light-transmissive electrode is between the substrate and the light-emissive elements of the OLED device, the device is called a bottom-emitting OLED device. Conversely, if the light-transmissive electrode is not between the substrate and the light-emissive elements, the device is referred to as a top-emitting OLED device.
The organic EL medium structure can be formed of a stack of sub-layers that can include small molecule layers and polymer layers. Such organic layers and sub-layers are well known and understood by those skilled in the OLED art.
Because light is emitted through an electrode, it is important that the electrode through which light is emitted be sufficiently light transmissive to avoid absorbing the emitted light. Typical prior-art materials used for such electrodes include indium tin oxide (ITO) and very thin layers of metal. However, the current-carrying capacity of electrodes formed from these materials is limited, thereby limiting the amount of light that can be emitted from the organic layers.
In top-emitting OLED devices, light is emitted through an upper electrode or top electrode which has to be sufficiently light transmissive, while the lower electrode(s) or bottom electrode(s) can be made of relatively thick and electrically conductive metal compositions which can be optically opaque.
In conventional integrated circuits, bus connections are provided over the substrate to provide power to circuitry in the integrated circuit. These busses are located directly on the substrate or on layers deposited on the substrate, for example on planarization layers. In complex circuits, multiple levels of bus lines are located over the substrate and separated by insulating layers of material. For example, OLED displays sold by the Eastman Kodak Company utilize multiple bus lines located on the substrate and on various planarization layers. However, these busses are not useful to provide power to the light transmissive upper electrode in an OLED device because conventional photolithographic techniques destroy the organic layers and thin upper electrode necessary for a top-emitting OLED device.
Co-pending, commonly assigned US Publication No. 2004/0253756, published Dec. 16, 2004, entitled “Method of Making a Top-Emitting OLED Device having Improved Power Distribution” proposes to solve this problem by employing a method of making a top-emitting OLED device that includes providing over a substrate laterally spaced and optically opaque lower electrodes and upper electrode busses which are electrically insulated from the lower electrodes; depositing an organic EL medium structure over the lower electrodes and the upper electrode busses; selectively removing the organic EL medium structure over at least portions of the upper electrode busses to reveal at least upper surfaces of the upper electrode busses; and depositing a light transmissive upper electrode over the organic EL medium structure so that such upper electrode is in electrical contact with at least upper surfaces of the upper electrode busses. This method will effectively provide power to the upper electrode. However, the selectively removed organic EL material may re-deposit in other areas of the EL medium structure.
In any ablative system, there is a problem with removal of the ablated material, which is formed as a plume of smoke and debris. It is possible for the generated debris to deposit, for example, on the optics or internal surfaces of the laser ablation apparatus, or on the substrate or ablated layers themselves. The collection of such debris on the optics would result in a reduction in the energy that the imaging device was able to deliver to the ablation medium, which could potentially give rise to underexposure and loss of ablating capability. Furthermore, the airborne ablated particles and fumes are likely to give rise to various environmental issues and health and safety hazards. It is clearly necessary to provide means by which such ablation debris may be satisfactorily controlled.
Several means for the collection of ablation debris are already known from the published literature. Typically, an extraction apparatus is provided which comprises a vacuum head for collection of the ablated debris at the point at which it is generated, and a length of ducting to transport the collected debris from the vacuum head to a gas-particle separator device that removes and collects the ablated particles from the effluent gas. For example, U.S. Pat. No. 6,629,375B2 entitled “Apparatus for collecting ablated material” issued Oct. 7, 2003, US20040051446 A1 entitled “Method and apparatus for structuring electrodes for organic light-emitting display and organic light-emitting display manufactured using the method and apparatus” published Mar. 18, 2004, W09903157 entitled “Laser Ablation Method to Fabricate Color Organic Light Emitting Diode Displays” published Jan. 21, 1999, and U.S. Pat. No. 6,683,277 B1 and U.S. Pat. No. 6,797,919 B1 both entitled “Laser ablation nozzle assembly” and issued Jan. 27, 2004 and Sep. 28, 2004 respectively, describe laser ablation systems having a variety of nozzle designs, filtering methods, and mechanical arrangements.
However, such apparatus generally suffers from problems associated with the deposition of collected debris that can severely impair efficiency, and the incorporation of additional, remedial, features is often necessary in order to alleviate these difficulties. Moreover, these apparatuses operate only in an atmosphere whereas many deposition and process manufacturing steps are carried out in a vacuum. In many production processes, for example those used for OLED device manufacturing, materials are deposited in a vacuum chamber and it is inconvenient or detrimental to place the device in a laser ablation chamber having an atmosphere suitable for an extraction apparatus as described in the prior art.
There is a need, therefore for an improved method and apparatus for selectively removing material from a surface at an improved rate and with reduced contamination in a vacuum chamber.